1. Field of the Invention
This application relates to three dimensional mapping systems and methods. More particularly, it concerns methods for providing 3D profiles of surfaces from a remote position, particularly in submarine locations, and new systems for obtaining such profiles without requiring use of complex image processing hardware.
2. Description of the Prior Art
Submarine searches, research, investigations and like operations present a host of problems unrelated to terrestrial activities. Since much of such submarine work must be accomplished in personnel operated submarines or remotely operated vehicles (ROVs) that isolate data gathering entities from relevant marine objects or surfaces, there is a continuing demand for advanced underwater systems and methods for ranging, size estimation, profiling, mapping, etc. (see U.S. Pat. Nos. 4,777,501; 4,914,460 and 4,948,258). The present invention provides improved systems and methods to help meet this demand.
Laser photogrammetric technology has been extensively applied to solving problems associated with submarine activities as mentioned above. However, laser photogrammetric systems used for marine research and other submarine work have typically been limited to those having only several sampling beams or points. Reasons for this trend involve tradeoffs between design parameters, such as available laser power, background illumination, camera response and the complexity of the signal interpretation scheme. In those applications where surfaces or objects are rough or where multiple objects are present, more thorough sampling is desirable to obtain accurate photogrammetric estimates. Simple continuous laser illumination spread into multiple beams becomes difficult to observe and differentiate in a typical video frame. Conversely, stripe illumination eliminates ambiguity in identifying specific structured lighting elements, but is difficult to handle using conventional processing methods. As a result, systems based on video cameras are less desirable (as opposed to specialized detection and scanning systems) when a large number of mapping elements is required. Exceptions include shape from shading methods, stereovision, and video moire techniques (see Blatt, Hooker & Caimi, Optics and Lasers in Engineering, March, 1992, pp. 265-278).
A limiting factor in all conventional imaging systems has been operation at extended ranges or in turbid water because of scattered light from suspended particles or water molecules within the common volume defined by the field of view of the detector and the field of illumination from the light source. This scattered light reduces the apparent contrast of the scene being viewed in conventional imaging systems resulting in a decrease in accuracy of any range estimate. The present invention addresses this limitation problem and provides a unique solution therefor.
In spite of the extensive prior work and developments with underwater systems for ranging, mapping, etc. as noted above, substantial improvements are needed to further advance 3D mapping of submarine surfaces and objects.